Idle Circuit Running Rich

1987 DX
209K miles (if the dash is original. 5 speed swap wasn’t done by me and the dash has definitely been tampered with to cover up the PRND lights)

Got home and looked down the carb to see solid streams of fuel going down both barrels. Looked to me like the float was stuck up and fuel pressure was just shoving fuel straight through the carb. Just pulled off the top hat and cleaned quite a bit of dirt from the bowl. Been using non ethanol gas to clean things out so I expected a mess in there. Everything looked normal and operated freely (no sticking, just smooth movement and no fuel inside the float). Only now, with everything put back together, it idles rough but I don’t see the streams of fuel going into the carb. So that leads me to believe it is running rich only on the idle circuit, but I am unsure what to do about that. I’ve read that the mixture screw is blocked off from the factory as it isn’t necessary to adjust. What could be causing a rich idle circuit? My only thoughts are possibly an old gasket but I don’t know which gasket would affect only the idle circuit. The top hat gasket looked to be sealing everywhere just fine, and I cleaned off the mating surface on the carb body.

Car drives down the road beautifully, no hiccups at all. Just idles like crap and stinks up the cat. Idles better if I create a vacuum leak, but that just increases RPM rather than smooth the idle (confirming for me that it is getting too much fuel at idle). Don't know how to check the idle circuit system but I'll keep looking

Seems to be an intermittent issue as of the next morning. Fired up smooth and idled well, no issues. I’ll see what happens after work though. I expect the issue will come back after a long enough drive.

Drove home great to but I’ve noticed the Er is doing some strange shit. Making all kinds of noise in the intake at idle, I know my vacuum hoses are 100% but going to double check the routing regardless.

Er?

Besides your float level I wonder if you have some fuel pressure creep most carbs dont need much fuel pressure to run. Higher the pressure more chance fuel pushes past the needle and seat.

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Originally Posted by InAccordance

Er?

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Gol dang phone thinks it’s so freaken smart. Meant EGR lol. And okay, yeah it’s a new pump I wonder if it’s providing too much pressure? Is the best way to check that just a pressure gauge at the end of the feed line at the carb? New pump and new filters by the way. Also, the float level is set right at the upper most level of the “ok” zone. Haven’t tried lowering it to see if it makes a difference yet.

I'd guess the needle valve is tired.

Okay, what are your thoughts behind it? Just a sticking needle whenever it decides to stick, and leaks a little extra in from time to time? I could see that

Talking carb I assume... if the egr starts acting up, dump it. Easy to do on carb ones... not so much on FI but doable.

I thought about it...I’ve done the EGR delete on the LXi, but with the way I planned on romping on the DX after a Weber 38 and a 272 cam swap, I figured leaving the EGR would help the 200K+ piston rings and cylinder walls. Though with the plugs out I can see a very healthy cross-hatch on the walls still so maybe I shouldn’t worry about cylinder temps so bad.

What’s easier about the EGR delete on the carb models? My only knowledge has been to weld the nut at the manifold shut (unless there’s a plug with that thread pitch I don’t know about) and make a block off plate for the EGR valve. What I don’t know about is the other box & valve in front of the carb right along the valve cover. I see it just bolts to the intake, does it come right out without a hole needing a block off plate?

Also, quick thought..

Shouldn’t carbed models have a vented gas cap? This one has a solid metal one like my lxi, and on hot days or with a low tank, opening the cap releases a bunch of pressure. In fact, when I had streams of fuel coming out of every hole down into both barrels (engine both running and shut off), I released fuel tank pressure by opening the cap and the fuel stopped pouring into the barrels. Every carbureted vehicle I’ve owned or worked on had a vented cap to either release pressure or prevent tank-vacuum. Don’t know, just a thought. Who’s got an LX or DX, what kind of gas cap do you have?

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Originally Posted by Fixedit

Also, quick thought..

Shouldn’t carbed models have a vented gas cap? This one has a solid metal one like my lxi, and on hot days or with a low tank, opening the cap releases a bunch of pressure. In fact, when I had streams of fuel coming out of every hole down into both barrels (engine both running and shut off), I released fuel tank pressure by opening the cap and the fuel stopped pouring into the barrels. Every carbureted vehicle I’ve owned or worked on had a vented cap to either release pressure or prevent tank-vacuum. Don’t know, just a thought. Who’s got an LX or DX, what kind of gas cap do you have?

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Leave it loose or drill a hole in it.

Easier because if you remove it off an fi model, itll throw an ecu code. Carb wont.
Mine has a solid metal cap, far as I know it's the original one. If you look at the backside of it, it has vent holes.
I do get pressure though but isn't too crazy. Mine is so heavily modified though I cant compare it to stock anymore. Like I dont have a return line anymore, etc etc

Ah okay well if they are vented then I won’t mess with mine. And shit I forgot about the code thing on the lxis, what does throw the light on for carbed models? I was surprised to see no blinking light on this car when I got it. Yeah man I like your build, if I could afford it I’d go that route. A Weber will have to do though haha.

Still just an intermittent problem. If it starts up rough, I can keep it alive and once it’s driven around for a bit the idle will be fine. But the opposite happens too, I’ll start up fine and idle smooth but a little driving and the idle with get rich and try to die and all that. Making a trip north to get some parts this month and I’ll just save for a Weber 38.

Carb wont throw a light on the dash, they do have a quasi ecu thing under the seat but all it does is control emissions functions, itll still run without it.

38/38 is a nice route. Good power gains and will give you room to add more. I was going to do it but I've always wanted side drafts so just had to go for it lol.

Have you pulled the carb apart? I'd wonder if the float or needle are sticking.

Yeah I just meant the ecu under the seat. It’s nice not having a blinking light for a change. I’d love side drafts too but a 38 and a delta 272 cam should be plenty for me haha. Yeah it’s a long mess of a paragraph but in the first post I mention pulling the top hat off. Everything was normal in there, no sticking. Finally getting to set the float today, will be interesting if a lower level will help prevent a rich idle. Anyone know which direction the screw goes for up and down for the float? I’ll figure it out on my own but it could save me a few minutes knowing before I dig in lol

Okay counterclockwise for up, clockwise for down (referring to the level of fuel). Again when I first opened things up today and checked the level in the sight glass, it filled up way past normal. Opened the gas cap to release a bunch of pressure and the level went back to its regular spot. Upon adjusting the float level though it of course began to leak from the screw, luckily I got the level lowered enough to my liking with the screw in a spot that doesn’t leak. Still covered the edges of the screw with some sealant to be safe though.

With the float level adjusted I went for a long drive and couldn’t get it to act up. We’ll see what it does tonight when I go into work. It’s gotta be something sticking. Probably a combination of the pressure and something sticking that makes this all intermittent. Though I would like to conquer this problem and learn all that I can from it, I’m satisfied with the car still running for now and will just look forward to the carb and cam swap.

Sounds like that pressure buildup is causing the float to stick open.

That's what what I'm thinking. Just have no idea why there's a problem with pressure at all though. Or is that kind of pressure normal, and it's just the old float/carb that can't handle it? Dunno. If I have the same issue after a carb swap, I guess we'll know lol

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Originally Posted by Fixedit

Okay, what are your thoughts behind it? Just a sticking needle whenever it decides to stick, and leaks a little extra in from time to time? I could see that

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Just not sealing well. Depending on how they fail, they can allow more fuel to enter the bowl than they should or not enough or both depending on the situation.

Quote:

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Originally Posted by Fixedit

Shouldn’t carbed models have a vented gas cap? This one has a solid metal one like my lxi, and on hot days or with a low tank, opening the cap releases a bunch of pressure. In fact, when I had streams of fuel coming out of every hole down into both barrels (engine both running and shut off), I released fuel tank pressure by opening the cap and the fuel stopped pouring into the barrels. Every carbureted vehicle I’ve owned or worked on had a vented cap to either release pressure or prevent tank-vacuum. Don’t know, just a thought. Who’s got an LX or DX, what kind of gas cap do you have?

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Vented gas caps went the way of the Dodo starting in the '70s when stringent smog standards were implemented across the country. Instead of venting through the cap, emissions controlled tanks vent through the charcoal canister via the evaporative emission control system (EVAP). That's a fancy way of describing a vent tube that connects to a cylinder full of charcoal. The system works well but does sometimes have trouble. When it fails, it can clog and cause excessive tank pressure or simply stop filtering altogether which will make your garage smell like fresh gas all the time. Some tank pressure is normal, but if it's causing problems, you should fix it. You can read up on the system online (there isn't much to it) and then follow the troubleshooting chart on p. 12-84 of the manual to fix it. You can also bypass it, but expect the car to smell like gas all the time if you do.

The alternative is that the EVAP system is working perfectly well, but your needle valves are no longer sealing sufficiently to overcome normal tank pressure. In that case, you need to replace them. Traditionally, that is done in the context of a complete carb overhaul because you have to remove so much stuff to get to them that it makes sense to refresh everything else at the same time. That's normal carbs, but these are the legendary Keihin carbs that strike fear into the hearts of mortal men. I've done battle with 2 other Keihin carbs (1 win and 1 horrible, horrible loss), but not a 3g carb, so I can't really say what your best strategy is. I would do an overhaul, but if you don't feel confident, don't have the time, can't find the parts, etc. and you can open the float bowl without disturbing a lot of other stuff, then a simple needle valve replacement may be your best option. I'd try to replace the seats as well (the big brass screws you turn to adjust the fuel level), because they could be damaged, which would make short work of your new valves. It is a good idea to replace any carb gaskets you open too.

https://itstillruns.com/causes-build...s-6899381.html

I know a lot of people can't wait to remove every smog control device on their cars, but those systems have a lot of usefulness beyond keeping the air clean. EVAP systems, for instance, keep your car from stinking. EGR, as another example, prevents pinging, which is good if you plan to advance your timing. It's worth learning about the various systems and how to repair them. Almost all of them have positive benefits for the engine.



And why is Photobucket desecrating my sig with their ugly watermark???

I had thoughts about the EVAP charcoal canister clogging and causing excess pressure, but as I typed it out I though “nah, that’d be too easy, sounds too good to be true,” and promptly deleted all that I typed hahah. It’s been on my to-do list to refresh my memory of the entire system so I can do some testing. Easy to forget to do that though when it decides not to act up for a couple days! And yeah see I really like the idea of the EGR taking care of cylinder temps if I’m going to lead-foot it the way I know I will after a Weber and cam swap. It seems to not be causing any issues but it’s making noise, which may or may not be normal I’m just not familiar with everything about carbed models yet.

I’ll test the EVAP to look for a difference in tank pressure and/or any improvement, then needle valves and deeper carb maintenance if I need to drive it longer before any swaps are done. If it can stay exactly the way it is right now for a while though I should be okay

I'll cross my fingers for you. LOL

Guess that's why I get pressure buildup, evap system is gone lol

I may be jinxing it but I thought I'd update. No issues since I adjusted the float...I'm thinking the non-ethanol just got the dirt-nasties through the system and had a hiccup along the way. I've been kind of helping it by releasing tank pressure at the fill cap before and after driving on warm days. Probably helps but I don't know for sure at this point. Saving up for that Weber 38...got a 272 cam coming for it and after the carb I'll go for a DC header. Wishful thinking lol...

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Originally Posted by InAccordance

Guess that's why I get pressure buildup, evap system is gone lol

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This thread has me thinking... is your vent line (where the evap plugged into on the tank) plugged? I deleted the evap and plugged the vent on a mercury cougar I had and the plastic tank imploded and crushed the fuel sender. if the evap clogging up is a possibility for pressure creep and a rich idle then it needs to vent. I get some crazy tank pressure in the summer and this never dawned on me, but Im kinda scared to vent it because I need all the fuel I can get to idle right lol, but Ive also never seen the afrs change after opening the tank or anything